1. Field of the Invention
The present invention relates to a reformer for a fuel cell using a partial oxidation reaction (also called autothermal) as a reforming reaction, and more particularly to a reformer for a fuel cell comprising a container provided with an inlet for introduction of a vapor of a methanol solution as a raw fuel and an outlet for discharge of a reformed gas, and a catalytic layer which divides the inside of the container into an inlet space communicating with the inlet and an outlet space communicating with the outlet end which is constructed such that a passing cross section of the catalytic layer at the side of the outlet space becomes larger than a passing cross section at the side of the inlet space.
2. Description of the Related Art
Although a reformer is often used for a conventional hydrogen supply apparatus to a fuel cell, for improvement of starting properties, responsiveness, and miniaturization, a reforming reaction using a partial oxidation method is effective in a conventional hydrogen generating apparatus as disclosed in Japanese Patent Unexamined Publication No. Hei. 8-231201.
In reforming by a partial oxidation reaction, a reaction in which excess water is added is generally used, and reaction proceeds according to the following equations, in which equation 1 indicates a partial oxidation reaction, equation 2 indicates a methanol decomposition reaction, and equation 3 indicates a shift reaction. EQU CH.sub.3 OH+0.5O.sub.2.fwdarw.CO.sub.2 +2H.sub.2 -192KJ (kilojoules) [Equation 1] EQU CH.sub.3 OH.fwdarw.CO.sub.2 +2H.sub.2 +91KJ [Equation 2] EQU CO+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2 -41KJ [Equation 3]
In an actual reforming unit, the partial oxidation reaction of methanol occurs, and the decomposition reaction of methanol progresses by heat generation in the former reaction, and the shift reaction occurs by CO obtained in the former reaction and excess water. In this case, while the partial oxidation reaction and the methanol decomposition reaction progress at a relatively high temperature of 300 to 400.degree. C., the shift reaction progresses at a relatively low temperature of, for example, 150 to 250.degree. C. so as to lower the unreacted CO concentration, and the reaction rate of the shift reaction is low as compared with the partial oxidation reaction and the methanol decomposition reaction. Thus the shift reaction determines the rate of the total reaction.
However, as the foregoing three kinds of reactions progress, the mole number of the reaction products at the right side of the above equations becomes larger than the mole number at the left side. Thus, the volume of the product gas increases, which causes the flow velocity to increase. That is, there is a problem that the flow velocity is increased in the region where the third shift reaction occurs, so that a sufficient shift reaction cannot be performed.
In a reforming unit using a partial oxidation reaction, heat supply from the outside is unnecessary, and for example, in the conventional hydrogen generating apparatus (Japanese Patent Unexamined Publication No. Hei. 8-231201), there is proposed a structure as shown in FIG. 10, in which a raw fuel is directly blown into a reforming unit K.
In the paper "REFORMERS FOR THE PRODUCTION OF HYDROGEN FROM METHANOL AND ALTERNATIVE FUELS FOR FUEL CELL POWERED VEHICLE" published August 1992 by Argonne National Laboratory Co. Ltd., as shown in FIG. 11, the JPL autothermal reformer is constructed such that a raw fuel gas, air, and water vapor are mixed by a swirl mixer SM, and are supplied in an axial direction of a cylindrical reforming unit in which a low temperature active catalytic layer L, an oxidation catalytic layer O, and a water vapor reforming catalytic layer H are arranged in sequence along the length of the reforming unit, so that the fed raw fuel gas is reformed.
In the above hydrogen generating apparatus, it is difficult to supply a raw fuel uniformly to the catalytic layers within the reforming unit, and so to effectively use the entirety of the catalytic layers, so that a sufficient shift reaction cannot be performed. Further, it is difficult to raise the volume velocity.
In the foregoing reformer, since the passage length of the cylindrical reforming unit through which a raw fuel gas passes is large, if a volume velocity, that is, a reaction gas flow amount per unit volume of a catalyst, which is an index of catalyst efficiency, is to be raised, the flow velocity becomes high and the pressure loss rises, so that the raw fuel must be introduced at a high pressure and high power consumption results.
Moreover, in order for the shift reaction to be sufficiently performed, the volume of the water vapor reaching the reforming catalytic layer for performing water vapor reforming reaction in FIG. 11 is required to be large, so that the pressure loss is further increased and the volume velocity is lowered.